Scientists believe a triple-risk model explains many SIDS cases: a baby has a defect in an area of the brain that controls breathing and arousal; the baby is at an age when those brain areas are immature; and the baby is exposed to an external stress that compromises his breathing or oxygen levels or causes overheating. “To have a SIDS death, you have to have at least one of those (factors), and you have a higher risk if you have two or three of those happening at the same time,” says Professor Fern Hauck of the University of Virginia School of Medicine.